The present invention relates to a spring clutch having a driving hub and a driven hub, the driven hub being rotated by the driving hub only when the clutch is engaged, and also including a spring coaxially fitted between the two hubs for torque transmission, and a clutch sleeve for the operation of the transmission.
Spring clutches are most frequently used as shifting clutches which, as a rule, are engaged and disengaged by way of an electromagnetically or mechanically-activated lever and a cam sleeve which interacts with the lever. Mostly, a transmission link is briefly interrupted when the clutch spring is opened by immobilizing the cam sleeve, thereby interrupting the transmission link between the driving hub and the driven hub. For this type of spring clutch with driving hub and driven hub normally standing in constant transmission link, the use of a helical spring results in a very simple construction. If, however, the opposite is the case and the transmission link is supposed to be present only when the clutch is activated, one can no longer make do with the simple constructional principle for such a spring clutch.
The present invention has to do with a spring clutch of the latter-named type, in which the transmission link is realized only during activation.
From GB-PS No. 898,183 a spring clutch is known which has a clutch sleeve surrounding the helical clutch spring, this sleeve, when the transmission link of the spring clutch is separated, being rotated by means of the helical clutch spring, which is applied with a segment with pre-loading against the drive hub and with another segment applied on the inside against the clutch sleeve. On the exterior circumference of this sleeve a helical control spring is fitted which rotates with the clutch sleeve, this control spring including an angled end which runs up against a radially displaceable activation lever so that by means of the clutch sleeve, which is held back by the control helical spring, the helical clutch spring is closed and the transmission link is established. The decisive disadvantage of this construction, however, consists in the fact that due to the form-closure between the spring and the clutch sleeve, friction and therefore wear-and-tear result between the sleeve and the control helical spring which sits on its perimeter while being held firmly by the activation lever during the starting phase, so that normally disengaged type spring clutch is suitable only for short starting phases and certainly not for high rates of revolution.